Not that she wasn't drop-dead gorgeous on a horse in Stepmom or, in Twilight, playing a piano -- but have you ever noticed how much time Susan Sarandon spends riding around in automobiles, like Kerouac or Lolita? For instance, Atlantic City, from which she escaped with Burt Lancaster. For further instance, Thelma & Louise, with Geena Davis in a Thunderbird convertible. And now, Earthly Possessions (Saturday, March 20; 8 to 9:45 p.m.; HBO), an amiable adaptation of Anne Tyler's 1977 novel, in which, in a succession of stolen cars, she dreams her way south as the complicit hostage of a hotheaded young loser who just happens to rob a bank where she's gone, in the first place, to withdraw getaway money in order to leave her husband.

It's a novel I like a lot. As usual in Tyler, an accidental tourist climbs aboard the wrong bus to circle among eccentrics who "made things look more interesting than they really were," as she wrote in Morgan's Passing, before arriving safely back for supper at the same old Homesick Restaurant. This wry fatalism can get on your nerves unless, like Sarandon's Charlotte, you go along to see if what happens next changes the pattern. By the time Stephen Dorff's feckless Jake finally liberates his pregnant girlfriend (Elissabeth Moss) from a holding cell for unwed mothers, he will realize he's been traveling with a woman but toward a child: "Charlotte," he says, "I can't quite manage without you just yet." And: "It ain't so bad if you're with us, see? You act like you take it all in stride, like this is the way life really does turn out. You mostly wear this little smile. I mean, we know each other, Charlotte. Don't we?"

Yes, they do. Some kidnapper; some hostage! Although director James Lapine and scriptwriter Steven Rogers love gas stations, biker bars, junk food, and country music as much as Tyler does, they've taken some odd liberties with the novel -- setting off in hot pursuit from New York instead of Maryland; calling it quits in South Carolina instead of Florida; changing the name of Charlotte's preacher-husband (Jay O. Sanders) from Saul to Zack and dropping his brother Amos, with whom she had an affair; omitting her mother, who was so fat that baby Charlotte came as a thundering surprise, and her child, who refuses in the novel to answer to her own name; and even her vocation as a photographer. This adds up to a huge subtraction from the number of earthly possessions Charlotte leaves behind. It threatens to render her almost as lightweight as Jake, a demolition-derby driver who blames everybody else for everything that's ever gone wrong in his fender-bender life.

Fortunately, to this half-Charlotte, Sarandon brings her Bull Durham comic timing and the heft of every other part she's played. Long before Jake's figured out that maybe he loves her, the rest of us are already standing in line. In a Chinese bowling alley, she marvels at a news program that features footage from the security camera in the bank where she was seized: "I never saw a room after I left it. It's so weird." If we've read the novel, we recall her mother's equally weird wondering: "It's amazing how every corner of the world agrees simultaneously that someone's dead. Don't you think so? I mean if a man dies in one room, then his meal in another goes untouched; he doesn't show up for his doctor's appointment . . . There's never a slip-up." Likewise, on gravity: "You'd think you could take gravity by surprise, just once, and set a tray very suddenly on air and have it stay. Wouldn't you?"

Even as she falls in a circle toward home, Susan Sarandon defies gravity. Of course, I'd prefer to believe that she'll keep on truckin', as she's been told to do by the button in the cereal box; that Earthly Possessions is really a prequel to Thelma & Louise; that after Jake has let her steer the "clown" car, and Zack imagines that he has at last taught her how to drive, she'll steal a Thunderbird and blast off into the ultimate lightness of western being, as if Big Sky and Monument Valley were landscapes of a wised-up female mind, the gaudy dreams of Mother Earth.